Prioritized list of potential culled satellite ephemeris information for quick, accurate assisted locating satellite location determination

ABSTRACT

Locating satellites (e.g., GPS) are culled into a preferred group having a longest dwell time based on a time passing through an ellipsoid arc path through a cone of space, and communicated to mobile devices within a particular region (e.g., serviced by a particular base station). The locating satellites may be culled into a prioritized list. Each satellite is assigned an order of precedence based on a remaining dwell time within a primary inverted cone. Thus, a number ‘N’ of satellite&#39;s ephemeris data may be used, along with a preferred ‘order of precedence’ for secondary satellites to be used as backups as necessary.

This application claims priority from U.S. Provisional Application60/618,606, filed Oct. 15, 2004, the entirety of which is expresslyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to wireless and long distance carriers,Internet service providers (ISPs), and information content deliveryservices/providers and long distance carriers. More particularly, itrelates to location services for the wireless industry.

2. Background of Related Art

It is desired to accurately locate cell phones within a cellularnetwork. While there are several techniques for determining location ina mobile device, a future generation of mobile phones may include aglobal positioning satellite (GPS) receiver chipset, thus having theability to locate itself via GPS.

FIG. 10 depicts the conventional Global Positioning Satellite systemincluding about 24 or more GPS satellites.

In particular, as shown in FIG. 10, the earth 200 is surrounded byapproximately 24 GPS satellites 101-124, which each have their ownrotational orbit about the earth 200. There are currently about 24 to 27GPS satellites in the GPS network, each moving about the earthapproximately 6 times each day.

Unfortunately, as the phone moves about the country, locations withrespect to satellites change. Thus, GPS devices attempting to determinetheir position with respect to the earth 200 will only be able tocommunicate with a smaller number of the total GPS satellites at any onetime.

The time required for lock in and location determination by aconventional GPS receiver in determining which of the GPS satellites inthe GPS network takes several minutes, and as many as 5 or 6 minutes fora standard GPS receiver, which is longer than many if not most phonecalls.

There is a need for a less cumbersome and more efficient technique forusing GPS location information in a highly mobile and fast pacedsociety.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a method ofculling a plurality of locating satellites into a sub-plurality forcommunication comprises culling a plurality of locating satellites intoa sub-plurality of a minimum preferred number of primary locatingsatellites. A remaining number of locating satellites that are not aprimary locating satellite are culled into a secondary sub-plurality oflocating satellites to be used as backups should any of thesub-plurality of primary locating satellites be unavailable.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present invention will become apparent tothose skilled in the art from the following description with referenceto the drawings, in which:

FIG. 1 shows a base station of a wireless network (e.g., a cellulartelephone network) determining which GPS satellites are in a preferredgroup, e.g., being within a cone of space with the longest dwell timewithin that space, in accordance with the principles of the presentinvention.

FIG. 2 shows a top view of the cone of space as shown in FIG. 1.

FIG. 3 shows vector calculations for each GPS satellite, or for each ofa preferred set of GPS satellites (e.g., those visible to the basestation), in accordance with the principles of the present invention.

FIG. 4 shows an exemplary culled GPS satellite table, in accordance withthe principles of the present invention.

FIG. 5 shows an alternate exemplary culled GPS satellite informationtable, in accordance with the principles of the present invention.

FIGS. 6A and 6B show use of the calculation of an ellipsoid arc pathactually traveled by each satellite to determine more accurately thelength of time a locating satellite is within range of a particularlocation, in accordance with another embodiment of the presentinvention.

FIGS. 7A, 7B(1) and 7B(2) show adjustment of the computation of the arcthat defines the inverted cone encompassing culled satellites as afunction of latitude, or distance from the equator, in accordance withyet another embodiment of the present invention.

FIG. 8 shows the utilization of wireless communication system cell citesas reference points, in accordance with a further embodiment of thepresent invention.

FIG. 9A(1) shows an exemplary culled locating satellite table includingprimary and secondary satellites, in accordance with an aspect of thepresent invention.

FIG. 9A(2) shows an alternative method of culling satellites byassigning a priority to each satellite within a given inverted cone,based on a remaining dwell time within the inverted cone, in accordancewith another aspect of the present invention.

FIG. 9B shows an alternate exemplary culled locating satelliteinformation table including visible, culled primary and secondary, andculled preferred (i.e., primary) locating satellites (e.g., GPSsatellites), in accordance with yet another aspect of the presentinvention.

FIG. 10 depicts the conventional Global Positioning Satellite systemincluding about 24 or more GPS satellites.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In a conventional GPS system, ephemeris data is provided to each GPSreceiver to keep track of where each of the satellites in the GPSsatellite network should be located in space. As part of the locationdetermination process, each GPS receiver determines which ofapproximately 24 or more GPS satellites are to be used to determine GPSlocation. This determination requires a significant amount of real-timeprocessing at the time of the location request, and a significant amountof time.

FIG. 1 shows a base station 150 of a wireless network (e.g., a cellulartelephone network) determining which GPS satellites 101-124 are in apreferred group, e.g., being within a cone of space 217 with the longestdwell time within that space, in accordance with the principles of thepresent invention.

In particular, as shown in FIG. 1, of the twenty four or so GPSsatellites 101-124 in the GPS system, only a sub-set 107-114 are visibleto the base station 150 at any one time. Thus, based on ephemeris data,the satellites communicating with a subscriber or user within a servicerange of the base station 150 may be culled to only those visible, e.g.,GPS satellites 107-114.

As a further culling, only those GPS satellites 109-113 currently withina cone of space 217 above the relevant base station 150 might beselected for communication with a receiver or subscriber within theservice area of the relevant base station 150.

As an ultimate culling, a minimum set of GPS satellites 109-112 may beselected based on, e.g., being not only within an arbitrary cone ofspace 217 normal to the base station 150, but also projected to remainwithin that cone of space 217 for the longest period of time, i.e.,having the longest dwell time. Thus, GPS satellite 113 may be eliminatedor culled from the minimum set of GPS satellites as it has almostcompletely passed through the cone of space 217, and will have theshortest dwell time of all GPS satellites within the cone of space 217.

Ideally, the cone of space 217 will be defined sufficiently large tocontain at least four GPS satellites at any one time. Alternatively, iffewer than the minimum GPS satellites are within the cone of space 217,then alternative selection criteria may be employed until sufficientnumber of GPS satellites enter the cone of space 217. For instance, aGPS satellite being closest to the cone of space may be utilized.

Updated ephemeris data is typically transmitted for one GPS satelliteeach second. Thus, for a GPS network of, e.g., 24 satellites, updatedephemeris data for all GPS satellites will have been transmitted after24 seconds. If the network is larger, e.g., 27 GPS satellites, allephemeris data will be transmitted after 27 seconds. Preferably, thesatellites will be periodically culled in accordance with the principlesof the present invention based on the provision of updated ephemerisdata, e.g., once every 24 seconds, once every 27 seconds, etc.

In accordance with the principles of the present invention, the totalnumber of available GPS satellites 101-124 is centrally culled for eachservice location, e.g., for each base station. The culling may begraduated, e.g., for each base station. The culling may be graduated,e.g., first down to those GPS satellites 107-114 that are visible, andthen down to a preferred minimum group (e.g., four (4) GPS satellites)having the longest dwell time for use by the particular cell site, orthe culling may be to some desired number of satellites all of which areannotated with an order of precedence indicator with which the mobiledevice can tell which is best, which is second best, etc. Of course, theculling may simply cull to a desired level (e.g., to a minimum of threeor four GPS satellites within the cone of space and having the longestdwell time) without graduation or indication of precedence.

When needed, the selected GPS satellites for a particular region at anyparticular time of request will be passed to requesting mobile devicesto help it determine its own location. For instance, each operativemobile unit is preferably periodically updated with a revised list ofselected GPS satellites resulting from the culling of the GPSsatellites, e.g., once after each new updated culled list of satellitesis determined. The information provided to each subscriber upon requestpreferably contains the identity of those GPS satellites that areselected for communication. However, information provided in the reversesense is also within the scope of the present invention (e.g., a list ofGPS satellites NOT to communicate with).

A wireless network may generate a flush of updated culled GPS satelliteinformation periodically, e.g., every 24 seconds. Note that based on thepositions of the various GPS satellites 101-124, and in particular basedon the positions of the selected GPS satellites 109-112 within the coneof space 217, the list of selected GPS satellites may or may not change.

Preferably, network traffic will be minimized by reducing or eliminatingredundant GPS satellite information. Thus, in a preferred embodiment,GPS satellite list updating messages are sent only when a change in thelist has occurred.

FIG. 2 shows a top view of the cone of space 217 as shown in FIG. 1.

In particular, as shown in FIG. 2, a cone of space 217 is viewed fromspace normal to a base station 150. On the ground, the base station 150has a service region 151. The circular representation of the conerepresents a plane cut across the cone of space 217.

Within the cone of space 217, GPS satellites 101-124 generally travelfrom one side to the other. Dwell time is determined based on a distancebetween the present location of the particular GPS satellite, and theexit edge of the cone of space 217, as well as the rate of speed of theGPS satellite.

A minimum dwell time may be defined and represented as a edge 218 shownin FIGS. 1 and 2.

A satellite velocity vector may be determined or predetermined.Satellite velocity vector as used herein refers to a vector whosemagnitude is the velocity of the satellite and whose origin is thesatellite's current position.

The satellite's velocity vector may be derived from the ephemeris datadescribing the satellite's orbit and current position. The satellite'svelocity vector provides the satellite's velocity and direction oftravel. The satellite's velocity and direction are used to compute thepoint of intersection of the satellite's orbit and the edge of the coneof visibility 217.

This computed point of intersection along the satellite's orbit definesthe endpoint of an ellipsoid arc from the satellite's current positionto the point of intersection. The satellite's velocity and orbitalparameters—provided by ephemeris data—can be used to compute the time itwill take the satellite to traverse that ellipsoid arc. This time valueconstitutes the satellite's dwell time within the cone of visibility.

It should be noted that GPS satellites have many different orbits, andalmost never travel in precisely the same direction as other GPSsatellites, as depicted by the various directions of the velocityvectors shown in FIG. 2.

In accordance with the principles of the present invention, a smallgroup of GPS satellites with the longest “cone” dwell times will beselected and some of the other GPS satellites will be “culled”. Thelongest dwell time relates to the amount of time that a calculated GPSsatellite vector will be within a respective cone of space 217 above aparticular region of users, e.g., above a particular base station 150.

The cone of space 217 may be simply a cone of visibility above the basestation 150, or may be more narrowly defined than visibility.

The resultant list of selected GPS satellites is preferably periodicallyand continually updated for any particular location, e.g., base station150, as the GPS satellites 101-124 rotate about the earth. Updatedselected GPS satellite lists are preferably communicated to thesubscriber's mobile device (or other suitable application location) fortheir respective calculations of accurate location information. With theuse of selected GPS satellites only by culling out unnecessary or unseenGPS satellites, the total time required for a mobile phone to locateitself can be reduced significantly, e.g., from minutes to just seconds.

FIG. 3 shows vector calculations for each GPS satellite 101-124, or foreach of a preferred set of GPS satellites (e.g., those visible to thebase station), in accordance with the principles of the presentinvention.

In particular, as shown in FIG. 3, conventional GPS ephemeris data isformatted as RINEX 2.10 data, which is provided by conventional GPSephemeris data vendors to a Gateway Mobile Location Center (GMLC) and/ormobile position center (MPC). In the preferred embodiment, a XypointLocation Platform (XLP) was used. In accordance with the principles ofthe present invention, received RINEX data is converted into an EarthCenter (EC) position vector (i.e., a vector pointing to the satellite'scurrent position whose origin is the center of the Earth). Then, usingthe Earth Center position vectors, the available GPS satellites areculled such that only desired GPS satellites are communicated with(i.e., those that will be in the cone of space 217 the longest).

In the disclosed embodiments, an Earth Center position vector iscomputed (or pre-computed) for every cell site 150 in a cellularnetwork. The cell site's EC position vector can be subtracted from theGPS satellite's EC position vector to arrive at a vector that pointsfrom the cell site 150 to the particular GPS satellite 101-124. Theresulting vector can be divided by its own magnitude to generate a unitvector that points from cell site 150 toward the particular GPSsatellite 101-124. The cell site's EC position vector can similarly bedivided by its own magnitude to generate a unit vector that pointsstraight up from the cell site 150 (also pre-computed).

The dot product of the GPS satellite pointing unit vector and thevertical unit vector yields the cosine of the angle between the twovectors. The cosine of an angle of zero degrees yields the value 1.0.The resulting value of the equation “cosine (angle)” diminishes as theangle grows until the cosine of 90 degrees yields the value 0.0. Thecosine of angles greater than 90 degrees yield negative results. Thismakes the cosine of the angle between the satellite pointing unit vectorand the vertical unit vector particularly well suited for identifyingwhether or not the satellite is “visible”. An angular measurementdefining a cone of space above the cell site (e.g., a “cone ofvisibility”) can be pre-computed as a function of the latitude at whichthe cell site is located. The cosine of this latitude derived angle canbe saved. Any satellite whose dot product with the vertical unit vectoryields a value greater than or equal to the saved cosine reference valuecan then be considered “visible”.

Thus, a rough culling of GPS satellites 101-124, e.g., to only thosevisible, or even better yet to only those most normal to a base station150, certainly culling out all GPS satellites that aren't visible atall, and reducing the number of GPS satellites with which to communicateto some small number, each of which is annotated with its order ofprecedence. This helps keep the time needed to determine location shortby providing “backup” satellites with which to communicate just in caselocal topography blocks the signal from a satellite with a longer dwelltime (e.g., a satellite with a lower “order of precedence” value).

FIG. 4 shows an exemplary culled GPS satellite table 100, in accordancewith the principles of the present invention.

In particular, as shown in FIG. 4, the selected group of satellites forany particular cell site may be maintained in a suitable database and/orother table 100, which may then be provided upon request to anyparticular mobile device within the service area of that particular cellsite 150.

Thus, a small subgroup of GPS satellites having the longest dwell timewith respect to a servicing cell site 150 are selected, and maintainedin a culled satellite table 100 communicated to all active mobilesubscribers (or other grouping of mobile users). Moreover, oralternatively, whenever a mobile device requires ephemeris data, it mayrequest an update to a culled satellite table 100 containing theidentity of the preferred satellites with which to use to determinelocation of the mobile device.

FIG. 5 shows an alternate example of a selected or culled GPS satelliteinformation table, in accordance with the principles of the presentinvention.

In particular, as shown in FIG. 5, a database or table 100 b may includeinformation regarding all or most GPS satellites 101-124, with thosethat are selected for any particular base station 150 beingappropriately indicated.

While the present invention is explained with reference to the use of asfew as three (3) or four (4) and as many as 24 or 27 availablesatellites 101-124, the present invention relates to the use of anynumber less than all GPS satellites.

Moreover, while the present invention provides culling of visiblesatellites, and even to a minimum number of satellites, e.g., down tofour from those visible satellites, the resultant number of satellitesmay be a number greater than or even less than 4, within the principlesof the present invention. For instance, if only position is required,only three (3) GPS satellites are required. However, if altitude is alsorequired, four (4) GPS satellites are the minimum required and thus themaximum culling level. Moreover, the use of more than approximately six(6) GPS satellites do not significantly improve the accuracy of theresults.

If a mobile device is unable for some reason to communicate with one ormore GPS satellites directed by the culled GPS satellite table orsimilar information, the mobile device may then attempt to achievelocation information in an otherwise conventional manner, e.g., byattempting contact with all GPS satellites.

The core technology of culling locating satellites to a sub-plurality isdisclosed in U.S. Pat. No. 6,650,288, co-owned with the presentapplication. The following sets forth several significant advances tothat core technology.

1) Compute Satellite Dwell Time Based on Ellipsoid Arc

FIGS. 6A and 6B show use of the calculation of an ellipsoid arc pathactually traveled by each satellite to determine more accurately thelength of time a locating satellite is within range of a particularlocation, in accordance with another embodiment of the presentinvention.

In particular, as described above, a satellite's path may be projectedonto a plane that, cutting through the inverted cone over a referencepoint, forms a circle. As described, the satellite's speed could be usedto approximate the satellite's dwell time within the cone. This is asimple function of computing the amount of time it would take thesatellite to traverse the chord cutting across the circle as if it wereactually traveling in a straight line.

However, a straight line in the plane cutting across the inverted conewould be an approximation. The satellite isn't actually traveling in astraight line, but rather in an ellipsoid arc.

In accordance with this embodiment, the dwell time is computed using thesatellite's actual ellipsoid arc, as well as the position of thesatellite with respect to the Earth (i.e., whether the satellite'saltitude is increasing or decreasing) to improve the selection process.

As shown in FIG. 6A, the orbit of a locating satellite is typicallyelliptical. The depiction in FIG. 6A is somewhat exaggerated inellipticity for ease of explanation. In the orbit, the point(s) at whichthe locating satellite is farthest from Earth is called the apogee ofthe orbit, while the point(s) at which the locating satellite is closestto the Earth is called the perigee of the orbit.

The present embodiment appreciates two aspects of the calculation ofsatellite dwell time that are not detailed in the prior art: theellipsoid arc path of the locating satellite through the inverted cone(as depicted in FIG. 6B), and the fact that the acceleration of thelocating satellite is decreasing as it moves on its orbit beyond perigeebut toward apogee, causing a decrease in the speed of the locatingsatellite with respect to the Earth. As the locating satellite moves inits orbit between apogee and perigee, the gravitational pull of theEarth causes an increasing acceleration, and thus an increasing speed.

The math involved in calculating the ellipsoid art passing through anygiven cross section of any given inverted cone (e.g., as shown in FIG.6B) is conventional, as is calculations of the acceleration and speed ofthe locating satellite on any given point of its orbit. It is therecognition and application of the actual path of the locating satelliteas well as its actual speed, rather than use of a straight lineapproximation, that is important to the principles of the presentembodiment of the invention.

2) Compute the Arc that Defines the Inverted Cone as a Function OfLatitude

FIGS. 7A, 7B(1) and 7B(2) show adjustment of the computation of the arcthat defines the inverted cone encompassing culled satellites as afunction of latitude, or distance from the equator, in accordance withyet another embodiment of the present invention.

In particular, as described above, an angle may be defined thatultimately defines a cone above the reference point. In accordance withyet another embodiment, that angle defining the cone may be selected orcomputed as a function of the reference point's latitude.

FIG. 7A depicts a cross-sectional view of Earth, with an imaginary basestation 707 located longitudinally on the equator. The angle A at thebase of the inverted cone defining locating satellites within view is ata minimum.

The present embodiment establishes inverted cones with a larger angle (Band C, respectively) as compared to the angle A of the inverted cone atthe equator. In this embodiment, the larger angles B, C of the invertedcones are established to be in a relationship to the latitude (e.g., thedistance from the equator of the Earth) of the relevant base station.

Thus, the closer the relevant base station is to the equator, the morelikely it is that a sufficient number of locating satellites will bevisible (e.g., 4 satellites visible). The farther the relevant basestation is from the equator, the fewer number of locating satelliteswould be visible within a same inverted cone.

Stated differently, the present embodiment establishes an inverted conehaving a larger base angle at a base station farther from the equator toencompass the same number of preferred or minimum culled locatingsatellites as would a base station located more closely to the equator.This is depicted in FIGS. 7B(1) and 7B(2).

In particular, FIG. 7B(1) shows a cross section of the inverted coneestablished to define the culling of locating satellites for a basestation 707. The base angle of the inverted cone has an angle A.

In comparison, as shown in FIG. 7B(2), a cross section of the invertedcone established to define the culling of locating satellites for a basestation 708 located farther from the equator than was base station 707shown in FIG. 7B(1). As depicted, at or near the equator thedistribution of satellites within the cone of visibility will likely befairly uniform. However, in locations significantly away from theequator, the distribution of visible satellites within the cone ofvisibility look tend to be nearer to one boundary or the other,depending on which hemisphere), rather than being uniformly distributedthroughout the inverted cone. Thus, as shown in FIG. 7B(2), in alocation away from the equator, the visible satellites tend to favor theedge of the inverted cone closest to the equator.

The present embodiment also appreciates that received signal strengthfrom the locating satellites is best when the locating satellite isdirectly overhead of the base station (i.e., normal to the Earth at thelocation of the base station). Thus, the inverted cone of ‘visible’locating satellites is made narrower when the base station is closer tothe equator of the Earth, and made larger when the base station isfarther from the equator of the Earth.

Thus, as appreciated by the present inventors, there are benefits tolimiting the span of the inverted cone if one's latitude doesn't force awider span just to see the GPS satellites.

3) Utilization of Cell Site Antennas as Reference Points

The embodiments thus far relate to the definition of a full invertedcone above a base station 150 (e.g., having 360 degree coverage). FIG. 8shows the utilization of reference points for locating satellites, inaccordance with a further embodiment of the present invention.

In particular, an inverted cone 217 is computed above given ‘referencepoints’ as an estimate for an inverted cone above the relevant wirelessdevice 150. In accordance with a further embodiment, the reference pointmay be a wireless communications cell site 860 (e.g., cell phone basestation antennas). Thus, cell sites 860 may be specifically used asreference points for culling the ephemeris information used to expediteAssisted GPS location determinations.

In order to enable the mobile handsets (i.e., cell phones, wirelessenabled PDAs, etc.) to quickly locate themselves, it is desired toprovide them with a good indication of with which satellites tocommunicate.

To give the handset the subset of satellites it should communicate with,a rough idea as to the location of all satellites is required. Such arough idea allows the choice of a subset of the satellites that have avery high probability of being visible to the handset.

The parent patent (U.S. Pat. No. 6,650,288) refers to the “rough” or“approximate” positions as “reference points”. However, in accordancewith this aspect of the invention, it is possible to use any point atall, as long as one is chosen that is easily and quickly picked, andthat is also fairly close to the mobile handset.

Cell sites are particularly well suited for use as reference points forcellular phones because every mobile handset must communicate with acell site in order to do even basic wireless functions, and all the cellsites have been surveyed such that their locations are known. Surveyingthe cell sites was necessary in the U.S. in order to provide Phase One(i.e. imprecise) location for enhanced 911 support so that data isreadily available. Though Asia's and Europe's Emergency Servicesmandates are different than that of the United States, the cell sites inthose areas are also surveyed so their locations are also available.

Since cellular phones connect to carrier's networks through cell sites,there is very little additional time necessary to use that cell site'slocation as a rough approximation of the handset's location for thepurposes of choosing a subset of locating satellites.

In some cases, a cell site may have several sectors but be representedby only one location. In other cases, a cell site may represent only onereceiver of a collection of receivers (see FIG. 8). In either case, themobile handset will be communicating with one and only one of the cellsites, and that cell site will have a surveyed location that will quitenicely approximate the handset's location for the purposes of selectinga subset of locating satellites.

4) Provide More than Four (4) Satellite's Ephemeris Data with an Orderof Precedence Indication

As described above, it is preferred that no more than four (4)satellite's ephemeris data would be delivered to a wireless handset. Inthis way, using too much Radio Frequency (RF) bandwidth is avoided,while providing the data necessary to achieve a good GPS fix forlatitude, longitude, and altitude too.

Sometimes, more than just four (4) satellite's data is sent to thehandset. Sometimes this is done so that the handset can perform its ownsatellite selection. Sometimes this is done to provide a fallback incase a particular handset is masked and cannot receive the signal of oneor more of the primary selections.

FIGS. 9A(1), 9A(2) and 9B show the use of more than 4 culled satellites,providing the identities of additional satellites for the wirelessdevice to use as backup satellites as necessary (e.g., when a culled,preferred satellite is masked and the wireless device cannot receive thesignal of that primary selection), in accordance with still anotherembodiment of the present invention. Thus, a number ‘N’ (‘N’ beinggreater than 1 or 2 or 4 or whatever) of locating satellite's ephemerisdata may be used, along with a preferred ‘order of precedence’, allowinga mobile device to use the desired minimum number of locating satellites(e.g., four (4) locating satellites) if available, but could fall backas necessary to the use of other locating satellites that are visiblebut still favorable.

FIG. 9A(1) shows an exemplary culled locating satellite table includinga list of a preferred number of primary satellites (e.g., 4 preferredsatellites). Additionally, the exemplary culled locating satellite tableincludes an identification of at least one or more secondary locatingsatellites.

Preferably, a priority is given to each of the secondary locatingsatellites such that the relevant mobile device will, as necessary,attempt to receive a signal from each of the secondary locatingsatellites in the prioritized order.

The mobile device may, depending upon the particular application,attempt contact with all secondary, tertiary, etc. locating satelliteslisted in the culled locating satellites table 100 c. However, it ismore preferable, to save network resources and time, that once asufficient number of locating satellites have been achieved, the need tocontact additional locating satellites becomes unnecessary and may beabandoned for that particular locating session.

FIG. 9A(2) shows an alternative method of culling satellites byassigning a priority to each satellite within a given single invertedcone, based on a remaining dwell time within the inverted cone, inaccordance with another aspect of the present invention.

In particular, all dwell times are simply computed (i.e., durationswithin the inverted cone of visibility defined over a particularreference point), and then pick ‘N’ number of satellites. The number ofsatellites picked may be, e.g., five, or six, or nine, or twelve, orwhatever, so long as there are more satellites picked then are necessaryto determine location as desired.

These ‘N’ satellites are then annotated with an integer precedencevalue. The satellite with the longest dwell time would be annotated witha precedence value of ‘1’. The satellite with the second longest dwelltime would be annotated with a precedence value of ‘2’. This would givethe mobile handsets an easy indication as to which satellites to limittheir position determination, and which satellites to attempt to utilizefirst, second, third, etc.

The assignment of precedence to satellites allows a mobile handset aviable fallback should one of the preferred four (4) satellites betemporarily obscured while attempting to determine the handset'slocation. In this case, the handset would timeout while attempting toreceive one (or more) of the preferred satellites' signal, and simplymove to the satellite in the list with the next lowest precedenceindicator.

FIG. 9B shows an alternate exemplary culled locating satelliteinformation table including visible, culled primary and secondary, andculled preferred (i.e., primary) GPS satellites, in accordance with yetanother aspect of the present invention. Thus, a complete picture of alllocating satellites that the relevant mobile device may possibly receivea locating signal from is provided to the mobile device, allowing themobile device itself decide which locating satellites are to becommunicated with, and in what order.

While the invention has been described with reference to the exemplaryembodiments thereof, those skilled in the art will be able to makevarious modifications to the described embodiments of the inventionwithout departing from the true spirit and scope of the invention.

1. A method of culling a plurality of locating satellites into asub-plurality for communication, comprising: culling a plurality oflocating satellites into a sub-plurality of a minimum preferred numberof primary locating satellites; and culling a remaining number oflocating satellites that are not a primary locating satellite into asecondary sub-plurality of locating satellites to be used as backupsshould any of said sub-plurality of primary locating satellites beunavailable.
 2. The method of culling a plurality of locating satellitesinto a sub-plurality for communication according to claim 1, wherein:said preferred number is
 4. 3. The method of culling a plurality oflocating satellites into a sub-plurality for communication according toclaim 1, wherein: said steps of culling are both performed in a wirelesscommunication system base station in communication with a relevantmobile device.
 4. The method of culling a plurality of locatingsatellites into a sub-plurality for communication according to claim 1,wherein: said steps of culling are both performed in a mobile device. 5.The method of culling a plurality of locating satellites into asub-plurality for communication according to claim 1, furthercomprising: passing an identity of said culled group of locatingsatellites comprising said primary sub-plurality and said secondarysub-plurality, to a mobile device.
 6. The method of culling a pluralityof locating satellites into a sub-plurality for communication accordingto claim 1, wherein each of said plurality of locating satellitescomprise: a Global Positioning Satellite (GPS).
 7. Apparatus for cullinga plurality of locating satellites into a sub-plurality forcommunication, comprising: means for culling a plurality of locatingsatellites into a sub-plurality of a minimum preferred number of primarylocating satellites; and means for culling a remaining number oflocating satellites that are not a primary locating satellite into asecondary sub-plurality of locating satellites to be used as backupsshould any of said sub-plurality of primary locating satellites beunavailable.
 8. The apparatus for culling a plurality of locatingsatellites into a sub-plurality for communication according to claim 7,wherein: said preferred number is
 4. 9. The method of culling aplurality of locating satellites into a sub-plurality for communicationaccording to claim 7, wherein: said means for culling said primarylocating satellites, and said means for culling said secondary locatingsatellites, are both comprised in a wireless communication system basestation in communication with a relevant mobile device.
 10. The methodof culling a plurality of locating satellites into a sub-plurality forcommunication according to claim 7, wherein: said means for culling saidprimary locating satellites, and said means for culling said secondarylocating satellites, are both comprised in a mobile device.
 11. Themethod of culling a plurality of locating satellites into asub-plurality for communication according to claim 7, furthercomprising: passing an identity of said culled group of primary locatingsatellites and an identity of said culled group of secondary locatingsatellites, to a mobile device.
 12. The method of culling a plurality oflocating satellites into a sub-plurality for communication according toclaim 7, wherein each of said plurality of locating satellites comprise:a Global Positioning Satellite (GPS).